Shorting device



N. N. O KUN SHORTING DEVICE July 2, 1940.

2 Sheets-Sheet 1 Filed March 29, 1937 ATTORNEY N. N. OKUN SHORTING DEVICE July 2, 1940.

Filed March 29, 1937 2 Sheets-Sheet 2 INVENTOR &

ATTORNEY Patented July 2, 1940 UNITED STATES:

PATENT OFFICE 6 Claims.

The present invention relates to short circuiting means for a repulsion induction electric motor and particularly is directed to a shorting device comprising an annular band of pivotally sus- .5 tained electrically conducting members or fingers held out of contact with the bars of the commutator of the motor during starting thereof to permit the motor to start on repulsion and subsequently the fingers have parts swung outwardl ly by centrifugal force after starting of the mogo ronment these particles enter the gap and contact the swingable shorting members. The fan of the motor also agitates this dust and as the members are thrown outwardly the particles of dust collect in the annular gap and also are ham- 25 mered against the bars of the commutator. Eventually at least a part of the gap between the shorting device and the commutator bars is filled and thus an intervening insulating or conducting layer of particles bridges in part or in .30 Whole the swingable shorting members and the bars of the commutator. Where the layer of particles is insulating material, for example, wood, dust or the like, even though the swingable shorting members are thrown outwardly by centrifugal force, they will not properly short circuit the commutator due to the intervening layer of particles. Hence at least a part of the armature circuit is open and therefore the curcurent that should have been shorted passes through the next adjacent bar of the commutator through a helicoidal conducting spring externally surrounding the short circuiting members or slugs designed to normally hold the latter out of contact with the bars of the commutator during starting or stopping of the motor. Therefore this spring is heated and loses its temper. It also needlessly stretches and parts thereof become deformed, thus losing its desired resilient qualities and consequently the required 50 effectiveness of the helicoidal spring is lost. It

follows the slugs do not readily leave the commutator as needed during stopping of the motor. Obviously this is a serious defect in certain of the prior art shorting devices.

155 Where the layer of particles builtup within the gap and against the swingable members or slugs is capable of conducting an electric current, they will cause a continuous short circuiting of the commutator even during the attempt of starting of the motor.. Consequently instead of the motor starting on repulsion and. subsequently operating inductively, these functions are eliminated since the conducting layer built up between the slugs and the commutator transform the motor to induction starting and therefore the 10 motor cannot start. Instead, arcing and sizzling takes place between the slugs and the commutator bars which pit, stick, and even short circuit before this action is necessary.

The present invention has as one of its objects the provision of a sealed short circuiting device wherein the swingable conducting members are maintained in a relatively clean condition by having the outer rim of the shell of the short circuiting device disposed in contact with the bars of the commutator thereby precluding the formation of a dust or particle collecting gap.

The invention has as another object the provision of a serviceable and improved shorting device wherein the electrical swingable members or slugs cooperate with an internally disposed but annular spring having its terminals disposed in slidable overlapping relation whereby in the stopped or starting relation of the motor this spring is expanded to hold the slugs out of en- '30 gagement with the commutator bars and after a predetermined speed of the motor is reached outer portions of the slugs short circuit the cornmutator while the lower portions thereof hold the spring in a contracted or compressed relation.

The invention has as a further object the provision of a novel but rugged short circuiting device in which an expandible and contractible spring is movably disposed against the lower terminals of the slugs and Within a cage constitut- 40 ing an electrical shield whereby at no time does appreciable induced or collected current of the cage or shell pass through the expandible and contractible spring and therefore the latter will not heat up due to electrical causes to lose its desired temper and resiliency.

Other objects, advantages, features, and aspects of the invention will be more readily understood when considered in the light of the following detailed description and the accompany- 5 of being out of contact with the commutator bars.

Fig. 2 is a transverse sectional view taken along the line 22 of Fig. 1, however illustrating the slugs in contact with the commutator bars and expandible and contractible lapped and electrically shielded spring contracted or compressed.

Fig. 3 is an enlarged fragmentary view of Fig. 2.

Fig. 4 is an enlarged fragmentary view of Fig. 1 showing the lapped spring expanded and the pivoted slugs out of engagement with the commutator.

Fig. 5 is a view similar to Fig. 4 however illustrating the slugs in contact with or shortening the commutator and the lapped spring contracted.

Fig. 6 is a view similar to Fig. l but illustrating a slightly modified slug supporting housing or cage comprising an insulating shell.

Fig. '7 is a sectional view of a modified but sealed shorting device particularly illustrating the pivoted slugs thereof normally held out of contact with the commutator bars by a spiral spring.

Fig. 8 is a fragmentary view of Fig. 7 showing the swingable slugs held in contact with the commutator bars due to centrifugal force and against the resistance of the spiral spring.

Fig. 9 is a sectional view taken on the line 9-3 of Fig. '7.

Fig. 10 is a fragmentary view of the slidable lap joint of the inner spring of the form according to Figs. l-6 inclusive at a time when the slugs are out of contact with the commutator bars in the normal expanded relation of the spring.

Fig. 11 is a fragmentary view of the slidable lapped connection or joint of the spring shown in Figs. 1-6 when slugs are in contact with the commutator bars during which time the spring is contracted.

Fig. 12 is a fragmentary view of a modified shorting circuiting device wherein stepped or toothed fulcrum rings pivotally sustain a plurality of annularly arranged slugs normally sustained out of engagement with the commutator bars by a lapped expandible and contractible spring.

Fig. 13 is a view similar to Fig. 12 however showing the slugs thereof in contact with or shorting the commutator bars and the lapped spring compressed.

Fig. 13 is a fragmentary transverse sectional view of Fig. 12.

Fig. 13 is a front elevational View of one of the slugs of Figs. 12-13% Fig. 14 is a fragmentary longitudinal sectional view of another form of shorting device according tothe invention.

Fig. 15 is a sectonal view taken on the line |5-l5 of Fig. 14 however illustrating the swingable slugs in position to short the commutator bars.

Fig. 15 is a fragmentary View of companion fulcrum rings for pivotally sustaining one side of the swingalole slugs of Figs. 14 and 15.

Fig. 16 is a longitudinal sectional view of another modification.

' Fig. 17 is a sectional view on the line ll-ll of Fig. 16 however showing the slugs swung to short the commutator.

Fig. 18 is a plan view of one of the pivotally sustained slugs shown in Figs. 16 and 1'7.

Fig. 19 is an elevational View of Fig. 18.

Fig. 20 is a fragmentary sectional view of a short circuiting device of the type well known in the art wherein the swingable slugs are held out of contact with the commutator bars by a normally contracted so called garter spring and Fig. 21 is a view similar to Fig. 20 however illustrating the slugs short circuiting the commutator and the garter spring expanded.

Illustrative of the several embodiments disclosed the short circuiting device is generally denoted A and is mounted to bodily rotate with shaft ill of a repulsion induction motor fixedly carrying commutator ll comprising a closed band of insulated conducting bars [2. In the form according to Figs. 1-5 inclusive the short circuiting device comprises a cage or housing 13 in the form of a metal cup shaped member con stituting a shell having annular outer wall 14 which includes an upper annular flange or rim l5 and a lower annular flange l5 which is frictionally or rigidly secured to shaft it while the upper flange I5 is straddled by and secured to a recessed insulating ring if of Bakelite, or the equivalent thereof. This insulating ring l'l' bears against the bars 12 of the commutator and hence particles of dust, grit or dirt, etc., are prevented from entering the interior of the short circuiting device.

Fixedly attached to annular flange or bushing 16 is a vertically disposed metal ring it having an overhanging annular overhanging fulcrum flange l9 and fixedly fastened to annular wall M of the shell 13 by spot welding or the like is an annular metal fulcrum flange 23.

Fulcrum flanges l9 and 2t pivotally support an annular band of spaced but swingable' electrically copper conducting members or slugs 2| each of which includes an intermediate reduced portion 22 defining spaced upper and lower shoulders 23. More particularly each slug 2! includes a tail portion 2% and an enlarged head portion Each of the tail portions 2 is provided if desired with an aperture 26 to decrease the mass thereof, the arrangement being such that in their pivoted relation the slugs may be considered as unbalanced since their greater mass resides in their head portions 525 and although unbalanced pivoted slugs are disclosed the invention is not limited thereto for if desired balanced slugs may be utilized.

As shown bushing I6 and ring if) of the shell l3 are held against the commutator H by a snap ring 2'! fixedly retained in a groove 28 of the armature shaft Iii. Also snap ring 21 aids to hold insulating ring l'i sealed against the commutator bars [2.

Arranged within shell 13 is a split annular flexible and resilient relatively thin metal band or leaf spring 23. This band is coiled into its annular form from an elongated and flat strip of spring steel or the like and comprises relatively elongated tapered ends or terminals 38 and 3! each terminating substantially in a transverse feathered edge (Figs. 2, 3, 10 and 11). These tapered ends are disposed in superimposed relation to provide a split and slidable lap joint.

'The annular flexible band 29 is normally expanded and cooperates with tail portions 24 of the annular band of swingable slugs to hold the weighted or unbalanced head portions thereof away from the bars of the commutator when the motor is in a stopping or starting relation. On starting and as the centrifugal force increases, the resistance offered by the lapped spring is progressively overcome and consequently tail portions 24 progressively contract the spring as the speed increases and ultimately the slugs are swung outwardly to simultaneously contact or short the bars of the commutator. In this particular instance apex portions 32 of the slugs 2| engage or short the bars of the commutator and hence after a predetermined speed is attained it is apparent that the armature of the motor operates inductively instead of in repulsion as during starting thereof until the predetermined speed is reached.

With the slugs swung out to short the commutator bars, the tail portions of the slugs now hold the normally expanded split spring 25: contracted or compressed. On stopping the motor falls below the predetermined speed. The head portions 25 lose their centrifugal force. By reason of their unbalanced relation they tend to fall by gravity. This action however is supplemented by the split spring 29 which again expands actuating the tail portions 24 thereof to swing their heads 25 away from the commutator bars and the motor is again operating on repulsion. The enlarged head portions of heads of the slugs have a greater mass than the tail portion and for purposes of description as previously set forth the heads may be considered as weighted and accordingly would store up greater momentum during rotation of the armature to fly out rapidly and correspondingly would lose their momentum readily during the stopping interval. By the present arrangement the heads of the slugs therefore respond promptly and with fidelity in the matter of shorting the commutator on starting of the motor or in leaving the commutator bars on stopping the heads of the slugs promptly leave the commutator bars aided of course by gravity and by the expansion of the lapped spring 29.

With the motor stopped, slugs 2| are disengaged from the commutator bars and are held in such relation by lapped spring 29 which is I now expanded to provide a movable lap joint as indicated in Fig. 10 constituted by the beveled superimposed slidalole ends or terminals 30 and 3|. In such relation upper stop shoulders 23 abut the fixed fulcrum rings or flanges l9 and 8 thereby serving to limit pivotal displacement of the heads of the slugs away from the commutator bars. On and after starting of the motor, the lapped spring 29 is contracted by the tail portions 24 of the slugs and upper stop shoulder 23 are slightly lifted from the fulcrum rings l9 and 20 while the head portions 25 of the slugs are in electrical engagement with the commutator bars l2 and the lap association of the beveled terminals is slightly lengthened (see Fig. 11)

The short circuiting device illustrated in Fig. 6, is identical to the form disclosed in connection with embodiment according to Figs. 1-5 inclusive except the insulating ring or shoe I! of the latter is eliminated and the shell I3 is of a suitable insulation, such as Bakelite, electrose or other insulating material having its upper flange l abutting the commutator bars while its lower pushing it abuts the commutator ll. Also in Fig. 6 fulcrum ring 26 is moulded or fixedly fastened to the insulating shell or cup l3 While ring I8 is anchored to bushing l6. annular flange i 5 is continuously in engagement with the commutator thus precluding the admission of undesirable particles within the insulating shell. In Fig. 6, the swingable slugs are out of contact with the commutator bars and are held in such relation by the normally expanded spring 29 since the motor is at rest.

With the form according to Figs. ?-9 inclusive the shorting circuiting device comprising the in- In Fig.

sulating cup shaped shell or casing 3 having a marginal but annular hollow head 35 defining an inner annular but enlarged channel 36 in which enlarged heads 3! of the annular band of slugs 2| are swingably disposed. These slugs are provided with intermediate attenuated portions 38 terminating in hollow eyes 39 pivotally mounted on ring 40 disposed in the inner annular channel 4| of the bushing 42 of the insulating shell I3.

In Figs. 7-9 intermediate portions 38 of each of the slugs 2| are provided with a recessed or concentric groove 44 adapted to cooperate with the annular inwardly overhanging stop rib A5 to limit outward displacement of heads 3? of the slugs when the motor is moving to a stopping position at which time lips 4% of the slugs retract or move away from the commutator bars by reason of outward thrust applied to the annular electrically conducting copper shoe ll which is continuously urged against fiat faces 38 of the intermediate attenuated portions 33 of the slugs 2| by the spiral or tapered spring 19 having its outer and largest convolution 56 disposed andv retained in an annular channel of the conducting shoe 4'! while the inner contracted convolution abuts the inner contracted end 52 of the tapered recess or cavity 53 in commutator support The contracted end of spring 43 also abuts the motor shaft I9 and thus is firmly held in place. With the motor at rest or moving to a stop position the floating copper shoe 4? holds the slugs out of contact with the commutator bars l2. In starting from a stop position and after a predetermined speed of the motor shaft has been reached, the centrifugal force imparted to the slugs overcomes the resistance otlfered by spring 49 and hence lips 46 contact or short the commutator bars until such time that the speed falls below the predetermined speed. Furthermore since the heads of the slugs have considerable mass, the momentum thereof rapidly increases or decreases depending upon the variations in speed and it follows that the slugs of Fig. 8, as in case of the slugs of Figs. 1-6 are readily responsive and therefore are positive and rapid in operation, that is, engage or disengage the commutator bars when required and promptly. Since the slugs 2| in each of the hereinbefore described forms have their heads of considerably greater mass than their lower portion, they may be considered as weighted.

In the form according to Figs. 12 to 13*, the several slugs 2| are pivotally mounted on annular flanges or rings I9 and 20 (Fig. 13 These rings however are ribbed or stepped as shown in Figs. 12 and 13 to define spaced teeth or apices 60 each comprising a relatively long wall 6| and a short wall 62. Toothed ring 20 is spot welded to wall M of shell I 3 while toothed ring I9 is a part of annulus I8 which is fixed to flange l6 of the anchored shell l3 and it is to be understood that sloping walls El and 62 of corresponding teeth 60 of flanges l9 and 20 are in alinement while the relative short sloping walls thereof serve as fulcrum means cooperating notched intermedial portion 22 of the conducting slugs 2| which according to Figs. 12-13 inclusive have their upper parts 63 flared outwardly and twisted or offset as shown to provide an upper face 65' adapted to engage or short circuit one or more commutator bars when swung outwardly due to centrifugal force. These slugs may be made in one piece but as shown they are formed by bending together two similarly shaped integrally interconnected plate members 65 after which the inner juxtapositioned faces are appropriately anchored together. In other aspects the short circuiting device of Figs. 12-13 is along the lines of the embodiment according to Figs. 1-5 inclusive.

In the case of the form illustrated in Figs. 14-15 the slugs 2| include expanded or flared twisted or offset heads and contracted or curved terminals or tail portions as shown while the intermediate portions thereof integrally carry trunnions or extensions 66 and 61, the former being pivotally disposed in spaced but annularly arranged openings 68 in the insulating shell l3 while extension El are rotatably disposed in bearings 68 formed in beaded rim or annular flange 10 of flange I8 and in bearing H of a cooperating complementary beaded annular flange or rim l2 overhanging ring 13 which together with ring it is retained in annnular recess "M in the insulating shell [3 and held against the commutator by the snap ring 21.

As in the case of the form according to Figs. 1, 5 and 13 the upper ends of the slugs 2i of Figs. 14 and 15 are heavier than their tail portions. In other words, the upper portions of the pivoted slugs may be considered as weighted or unbalanced in respect to respective tail portions which are carried as shown in abutting relation with the split spring 29 and as in the case of the swingable slugs 2i of Figs. 12-13% the slugs in Figs. 14 and 15 although each is of one piece, the upper flared portions are twisted or offset in respect to their tail portions.

With the form shown in Figs. 16 to 19 inclusive the several slugs 2! are formed of sheet metal each bent back on itself to juxtaposition complementary sections and 8f which may be appropriately fastened together and constitute a curved tail portion 82, an intermediate hollow bearing 83 and an offset or twisted head E l each of which is angularly disposed in respect to its bearing to present a relatively wide upper curved surface 85 adapted to contact one or more commutator bars when thrown outwardly. Each slug or finger 2| of Figs. 16 and 17 have trunnions or pins 86 and 81 pivotally fastened to the insulating shell l3 and to a metal ring 38 fastened to the collar or bushing 90 of shell I3 by suitable bolt or rivet iii.

In each and every one of the forms disclosed in Figs. 1, 6, and 13-17, a normally expanded split spring cooperates with the tail portions of the swingable slugs to hold them spaced from the commutator and since the slugs are unbalanced in respect to their fulcrumed support because of their relatively heavy head portions they readily move away from the commutator bars by gravity when the motor slows down in stopping thus permitting the split spring 29 previously held contracted to readily expand. It follows that the action of gravity is supplemented by the expansion of the spring 29 and therefore the slugs promptly leave the commutator bars on stopping of the motor. On starting of the motor the added weight in the heads of the slugs permit the latter to move outwardly and promptly to short the commutator due to the increased centrifugal force.

It should be understood and appreciated that in each and every one of the forms disclosed the shell or casing in which the swingable slugs are sustained is sealed against the commutator and accordingly no dust, dirt or grit may enter the shell after the latter has been properly attached and retained on the motor shaft. Therefore the slugs are shielded to provide relatively clean contact with the commutator bars. As another advantage it is observed that the split and overlapped spring according to the invention is electrically shielded from carrying an electric current and in fact carries no appreciable current and hence is not heated whereby its temper is destroyed. For according to the forms of the invention disclosed in Figs. 1-6 and 12-17 the current carried by the slugs when shorting the cormnutator is directed away from the split overlapped spring as for example in Fig. 5 where ring l8 conducts the current from the commutator to the bushing it and ultimately to ground without reaching the lapped spring 2%, and in the case of the form of Figs. 7-9, the copper shoe 4'! is of low re- .sistance whereas the steel helicoidal spring 49 is of relative high resistance and therefore the copper shoe i'i carries the maximum amount of current when the commutator is shorted and spring 29 carries almost a negligible amount of current. Therefore the slug actuating springs 29 and 49 shown may be considered as electrically shielded and cannot heat up sufficiently to lose its temper and consequently its normal resiliency.

To appreciate the problem solved attention is directed to a conventional and prior art shorting device shown in Figs. 20 and 21. In these views dumb bell slugs ill have one end pivotally disposed in a bead 92 of an annular metal shell or ring it fastened to an annular metal bushing 93 which includes an annular stop rib 94 against which intermediate restricted parts 95 of the dumb bell slugs 2i are held by a normally contracted helicoidal annular or garter spring 96 when the motor is stopped. When starting and after a predetermined speed is reached the inner ends of the slugs short or engage the commutator bars it. However in practice, it has been found that the slugs 2| in pivoting after starting of the motor lift from rib 94, that is, their intermediate parts 95 to provide therewith a gap El'l (Fig. 21). Therefore the major part of the current from the commutator flows into the slugs and into the garter spring 96 and only a relatively small amount of the current flows through casing 13. Since therefore the major part of the current from the commutator flows through spring 96 and when the shorting slugs are contacting the commutator bars, spring 96 heats up excessively at various points losing its temper and consequently its desired resiliency needed to effectively close the slugs when the motor is stopping. Not only has it been found that the garter spring loses its temper but it burns out in several spots when it is carrying appreciable current from the commutator. At any rate in the prior art device referred to the garter spring is not electrically shielded and furthermore it is subjected to dirt, dust and grit which enters the open annular gap 18 formed between the commutator and the upper rim 99 of the metal shell l3 and as previously alluded to with dirt, grit or dust fastened to a slug then its adjacent slugs carry more current than required and. accordingly the garter spring becomes electrically overloaded above the ineffective current carrying slug. It therefore heats up and loses its temper at this point, thus reducing the efficiency thereof. In the example just referred to it was assumed that the dirt, grit, dust or the like was insulating. Where however it is of the conducting type, the commutator will be shorted before intended and the motor will not start nevertheless in this case also the garter spring carries appreciable heating current. Contrasting these disadvantages with the advantage of the shorting embodiments herein disclosed and according to the invention, no dirt, dust or grit can enter the slug sustaining annular chamber within the protective shell I3 and hence the slugs 2| therein are electrically free of any undesirable particles to impair their effectiveness and in all of the embodiments disclosed the slug actuating spring is electrically shielded, a decided advantage to prevent undesirable heating thereof due to electrical causes.

It is to be understood that the strength of springs 29 or 49 control the action of the slugs to permit the latter to short at a predetermined speed or within the range of the predetermined speed for which the motor is designed. For example short circuiting devices herein disclosed are employed on two, four or six pole, etc., A. C. repulsion induction motors. With a two pole motor, a relatively heavy slug closing spring is required; with a four pole motor, a less heavier type of spring is employed, and with a six pole even a lighter spring is employed. The resistance of the slugs actuating spring normally tending to close or hold the slugs away from the commutator is progressively overcome as the speed of the motor increases and at a certain speed of the motor these slugs will short circuit. It is this certain speed which heretofore has been designated as the predetermined speed or within the range of the predetermined speed and for purposes of description the last two expressions may be considered as having the same meaning and of course the predetermined speed of the motor at which time the slugs short the commutator varies with the character of the strength of slug actuating spring employed.

While the invention has been described in detail and many embodiments and a specific application thereof have been referred to, the invention herein is not limited to such specific application or to any such specific embodiments and it is to be understood that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a short circuiting device for a motor commutator, a shell adapted to be mounted on the shaft of said motor, a plurality of slugs, means within said shell for pivotally supporting said slugs, a sealed connection between said shell and commutator to prevent particles of dirt or dust to reach said slugs, a split and normally expanded annular leaf spring having overlapped terminals disposed in contact and slidable relative to each other, said spring cooperating with inner ends of said slugs to hold the latter normally out of contact with the bars of said commutator, and an electrical shield to prevent appreciable heating of said spring.

2. In a short circuiting device for a motor commutator, a shell adapted to be mounted on the shaft of said motor and having a plurality of swingable slugs therein, and an expandible and contractible relatively thin and split annular spring yieldingly abutting the inner ends of said slugs to hold the latter away from said commutator, said spring comprising a lapped connection having superimposed terminals disposed in slidable contactual relation for contracting said spring to permit the outer ends of said slugs to contact said commutator after starting of said motor and adapted on stopping of said motor to permit expansion of said spring whereby the latter holds said slugs out of contact with said commutator.

3. In a short circuiting device for a motor commutator, a shell adapted to be mounted on the shaft of said motor and having a plurality of swingable slugs therein, and an expandible and contractible split annular leaf spring cooperating with said slugs to hold the latter away from said commutator, said spring comprising a lapped connection having superimposed terminals disposed in slidable and contactual relation to permit contraction of said spring to hold said slugs in contact with said commutator after starting of said motor and adapted on stopping of said motor to permit expansion of said spring whereby the latter holds said slugs out of contact with said commutator, said shell being of insulation and in contact with said commutator to provide a sealed connection therewith, and an electrical shield to prevent appreciable heating of said spring.

4. In a short circuiting device for a motor commutator, a shell adapted to be mounted on the shaft of said motor and having a plurality of slugs each comprising a head having means adapted to short one or more bars of said commutator, an intermediate portion, and a tail portion, means for pivotally supporting said intermediate portions, and a normally expanded spring yieldingly abutting said tail portions to hold said head portions away from said bars on starting or on stopping of said motor, said spring having terminals disposed in overlapping and slidable re lation and adapted to shift circumferentially for contracting or expanding said spring during stopping or starting of said motor.

5. In a short circuiting device for a motor commutator, a shell adapted to be mounted on the shaft of said motor and having a plurality of slugs each comprising a head having means adapted to short one or more bars of said commutator, an intermediate portion, and a tail portion, means for pivotally supporting said intermediate portions, and a spring cooperating with said tail portions to hold said head portions away from said bars on starting or on stopping of said motor, said spring being normally expanded and having overlapped slidable terminals shiftable relative to each other and cooperating with several of said tail portions to urge several of said head portions away from said bars, said tail portions on starting of said motor cooperating to progressively contract said spring upon increased centrifugal force stored up in said slugs, said spring on stopping of said motor expanding to actuate said tail portions to permit said head portions to move away from said bars.

6. In a shorting device for a motor commutator, a shell, a plurality of conducting members within said shell, means for pivotally supporting said members, and a normally expandible coiled spring yieldingly abutting the inner ends of said members to hold the outer ends thereof away from said commutator, said spring having ends slidable relative to each other and in contact with each other to define an overlapped connection permitting said inner ends to contract said spring on starting of said motor to permit said outer ends to reach and movably engage said commutator.

NATHANIEL N. OK'UN. 

